Despite two-decade long HIV prevention efforts, recent reports suggest that new HIV infections are on the rise in the United States (CDC, 2008). This finding has sparked fears among public health professionals that another HIV outbreak may be imminent. To combat this, many researchers believe that we must achieve a greater understanding of the motivations behind sexual risk-taking in order to develop targeted HIV-prevention interventions. This study aims to address the National Institute for Mental Health's call for HIV prevention research by using a novel theoretical perspective to investigate HIV risk-taking behavior among university and community adults: Self-Determination Theory (SDT). SDT states that all individuals must fulfill their basic psychological needs of autonomy, competence, and relatedness to achieve optimal well-being and personal growth. I argue that when these needs are not fulfilled, individuals will turn to maladaptive coping mechanisms to reinstate need fulfillment back in their lives. I also believe that psychological distress and endorsement of aversive sex motives will also play a role here. Specifically, I believe that individuals suffering from acute need deprivation and experiencing psychological distress will be more likely to endorse avoidant 'sex to cope'motives which will then lead to greater sexual risk behavior. To investigate this hypothesis, 160 individuals will be recruited from university and community public health clinics to participate in a longitudinal diary study. Every week for five weeks, participants will fill out assessments asking them to describe their need satisfaction, psychological distress, endorsement of sex motives, and participation in sexual risk behavior over the past week. Data will be analyzed using multilevel modeling techniques to ascertain whether fluctuations in need satisfaction, psychological distress, and compensatory sex motives are related to fluctuations in HIV-related sexual risk behavior. PUBLIC HEALTH RELEVANCE: This study aims to use a major theory of motivation, Self-Determination Theory, to address one of the top public health concerns facing the US and the world: the transmission of HIV. Specifically, we will investigate why people participate in sexual risk behaviors by assessing the role of basic need satisfaction, psychological distress, and endorsement of aversive sex motives in the decision to engage in these behaviors. It is hoped that by using psychological theory to understand the dynamics involved in HIV risk behavior, we can develop targeted and efficient interventions to curb the spread of HIV.